Fix regression, BACKEND_URL now only processed at request-time

Former-commit-id: da14f44e910786e9e21b5968b77e97a94f2876ab

.claude/settings.local.json

@@ -0,0 +1,16 @@
+{
+  "permissions": {
+    "allow": [
+      "Bash(git checkout:*)",
+      "Bash(git add:*)",
+      "WebFetch(domain:localhost)",
+      "Bash(curl -s http://localhost:8000/api/settings/api-keys | head -50)",
+      "Bash(docker ps:*)",
+      "Bash(docker compose:*)",
+      "Bash(sleep 3 && curl -s http://localhost:3000/api/settings/api-keys | head -c 200)",
+      "Bash(sleep 4 && curl -s http://localhost:3000/api/settings/api-keys | head -c 200)",
+      "Bash(git commit:*)",
+      "WebSearch"
+    ]
+  }
+}

.mise.local.toml

@@ -0,0 +1,5 @@
+[env]
+AIS_API_KEY="***REMOVED***"
+OPENSKY_CLIENT_ID="***REMOVED***"
+OPENSKY_CLIENT_SECRET="***REMOVED***"
+BACKEND_URL="http://localhost:8000"

frontend/Dockerfile

@@ -11,10 +11,6 @@ WORKDIR /app
 COPY --from=deps /app/node_modules ./node_modules
 COPY . .
 ENV NEXT_TELEMETRY_DISABLED 1
-# NEXT_PUBLIC_* vars must exist at build time for Next.js to inline them.
-# Default empty = auto-detect from browser hostname at runtime.
-ARG NEXT_PUBLIC_API_URL=""
-ENV NEXT_PUBLIC_API_URL=$NEXT_PUBLIC_API_URL
 RUN npm run build
 
 FROM base AS runner

frontend/next.config.ts

@@ -1,9 +1,9 @@
 import type { NextConfig } from "next";
 
-// BACKEND_URL is a plain (non-NEXT_PUBLIC_) env var read at server startup —
-// not baked at build time — so it can be set in docker-compose `environment`.
-// Defaults to localhost for local dev where both services run on the same host.
-const backendUrl = process.env.BACKEND_URL ?? "http://localhost:8000";
+// /api/* requests are proxied to the backend by the catch-all route handler at
+// src/app/api/[...path]/route.ts, which reads BACKEND_URL at request time.
+// Do NOT add rewrites for /api/* here — next.config is evaluated at build time,
+// so any URL baked in here ignores the runtime BACKEND_URL env var.
 
 const nextConfig: NextConfig = {
   transpilePackages: ['react-map-gl', 'mapbox-gl', 'maplibre-gl'],
@@ -14,14 +14,6 @@ const nextConfig: NextConfig = {
   eslint: {
     ignoreDuringBuilds: true,
   },
-  async rewrites() {
-    return [
-      {
-        source: "/api/:path*",
-        destination: `${backendUrl}/api/:path*`,
-      },
-    ];
-  },
 };
 
 export default nextConfig;